1. Field of the Invention
The present invention relates to an image processing apparatus for electrically processing an original image.
2. Related Background Art
Image processing apparatuses such as facsimile systems are conventionally available which photoelectrically read original images and electrically process read image signals. In such an image processing apparatus, digital processing has recently come to be employed, due to its relative simplicity and its resistance against influence of external noise. For such processing, however, original images must be correctly converted into digital image signals.
Original images to be read have various states or characteristics (density, size and the like), and they cannot all be processed by a single processing method. In view of this, the operator must first determine the type of an original image and then adjust the image processing. However, such an adjustment is cumbersome and may result in an erroneous adjustment.
It can therefore be proposed to incorporate in an image processing apparatus a function for detecting the state of an original image and for automatically performing image processing suitable for each original image. With this method, the operator need not perform the adjustment described above, and an operator who is not accustomed to operation of image processing apparatus in general can perform image processing with ease and accuracy.
When, however, an original image density is detected and the image is digitized by such automatic processing, contamination or dust or the like on the original surface other than the image to be read may also be detected and may result in digitization errors.
When the maximum and minimum values of a density of an original image are detected to perform digitization of the image, the maximum and minimum values detected in a black or white solid image region or a halftone image region significantly differ from those of the overall image. When the former maximum and minimum values are used, digitization errors also occur.